/* $NetBSD: sys_select.c,v 1.39 2014/04/25 15:52:45 pooka Exp $ */ /*- * Copyright (c) 2007, 2008, 2009, 2010 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Andrew Doran and Mindaugas Rasiukevicius. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * Copyright (c) 1982, 1986, 1989, 1993 * The Regents of the University of California. All rights reserved. * (c) UNIX System Laboratories, Inc. * All or some portions of this file are derived from material licensed * to the University of California by American Telephone and Telegraph * Co. or Unix System Laboratories, Inc. and are reproduced herein with * the permission of UNIX System Laboratories, Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)sys_generic.c 8.9 (Berkeley) 2/14/95 */ /* * System calls of synchronous I/O multiplexing subsystem. * * Locking * * Two locks are used: and selcluster_t::sc_lock. * * The might be a device driver or another subsystem, e.g. * socket or pipe. This lock is not exported, and thus invisible to this * subsystem. Mainly, synchronisation between selrecord() and selnotify() * routines depends on this lock, as it will be described in the comments. * * Lock order * * -> * selcluster_t::sc_lock */ #include __KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.39 2014/04/25 15:52:45 pooka Exp $"); #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* Flags for lwp::l_selflag. */ #define SEL_RESET 0 /* awoken, interrupted, or not yet polling */ #define SEL_SCANNING 1 /* polling descriptors */ #define SEL_BLOCKING 2 /* blocking and waiting for event */ #define SEL_EVENT 3 /* interrupted, events set directly */ /* Operations: either select() or poll(). */ #define SELOP_SELECT 1 #define SELOP_POLL 2 /* * Per-cluster state for select()/poll(). For a system with fewer * than 32 CPUs, this gives us per-CPU clusters. */ #define SELCLUSTERS 32 #define SELCLUSTERMASK (SELCLUSTERS - 1) typedef struct selcluster { kmutex_t *sc_lock; sleepq_t sc_sleepq; int sc_ncoll; uint32_t sc_mask; } selcluster_t; static inline int selscan(char *, const int, const size_t, register_t *); static inline int pollscan(struct pollfd *, const int, register_t *); static void selclear(void); static const int sel_flag[] = { POLLRDNORM | POLLHUP | POLLERR, POLLWRNORM | POLLHUP | POLLERR, POLLRDBAND }; static syncobj_t select_sobj = { SOBJ_SLEEPQ_FIFO, sleepq_unsleep, sleepq_changepri, sleepq_lendpri, syncobj_noowner, }; static selcluster_t *selcluster[SELCLUSTERS] __read_mostly; static int direct_select __read_mostly = 0; /* * Select system call. */ int sys___pselect50(struct lwp *l, const struct sys___pselect50_args *uap, register_t *retval) { /* { syscallarg(int) nd; syscallarg(fd_set *) in; syscallarg(fd_set *) ou; syscallarg(fd_set *) ex; syscallarg(const struct timespec *) ts; syscallarg(sigset_t *) mask; } */ struct timespec ats, *ts = NULL; sigset_t amask, *mask = NULL; int error; if (SCARG(uap, ts)) { error = copyin(SCARG(uap, ts), &ats, sizeof(ats)); if (error) return error; ts = &ats; } if (SCARG(uap, mask) != NULL) { error = copyin(SCARG(uap, mask), &amask, sizeof(amask)); if (error) return error; mask = &amask; } return selcommon(retval, SCARG(uap, nd), SCARG(uap, in), SCARG(uap, ou), SCARG(uap, ex), ts, mask); } int sys___select50(struct lwp *l, const struct sys___select50_args *uap, register_t *retval) { /* { syscallarg(int) nd; syscallarg(fd_set *) in; syscallarg(fd_set *) ou; syscallarg(fd_set *) ex; syscallarg(struct timeval *) tv; } */ struct timeval atv; struct timespec ats, *ts = NULL; int error; if (SCARG(uap, tv)) { error = copyin(SCARG(uap, tv), (void *)&atv, sizeof(atv)); if (error) return error; TIMEVAL_TO_TIMESPEC(&atv, &ats); ts = &ats; } return selcommon(retval, SCARG(uap, nd), SCARG(uap, in), SCARG(uap, ou), SCARG(uap, ex), ts, NULL); } /* * sel_do_scan: common code to perform the scan on descriptors. */ static int sel_do_scan(const int op, void *fds, const int nf, const size_t ni, struct timespec *ts, sigset_t *mask, register_t *retval) { lwp_t * const l = curlwp; selcluster_t *sc; kmutex_t *lock; struct timespec sleepts; int error, timo; timo = 0; if (ts && inittimeleft(ts, &sleepts) == -1) { return EINVAL; } if (__predict_false(mask)) sigsuspendsetup(l, mask); sc = curcpu()->ci_data.cpu_selcluster; lock = sc->sc_lock; l->l_selcluster = sc; if (op == SELOP_SELECT) { l->l_selbits = fds; l->l_selni = ni; } else { l->l_selbits = NULL; } for (;;) { int ncoll; SLIST_INIT(&l->l_selwait); l->l_selret = 0; /* * No need to lock. If this is overwritten by another value * while scanning, we will retry below. We only need to see * exact state from the descriptors that we are about to poll, * and lock activity resulting from fo_poll is enough to * provide an up to date value for new polling activity. */ l->l_selflag = SEL_SCANNING; ncoll = sc->sc_ncoll; if (op == SELOP_SELECT) { error = selscan((char *)fds, nf, ni, retval); } else { error = pollscan((struct pollfd *)fds, nf, retval); } if (error || *retval) break; if (ts && (timo = gettimeleft(ts, &sleepts)) <= 0) break; /* * Acquire the lock and perform the (re)checks. Note, if * collision has occured, then our state does not matter, * as we must perform re-scan. Therefore, check it first. */ state_check: mutex_spin_enter(lock); if (__predict_false(sc->sc_ncoll != ncoll)) { /* Collision: perform re-scan. */ mutex_spin_exit(lock); selclear(); continue; } if (__predict_true(l->l_selflag == SEL_EVENT)) { /* Events occured, they are set directly. */ mutex_spin_exit(lock); break; } if (__predict_true(l->l_selflag == SEL_RESET)) { /* Events occured, but re-scan is requested. */ mutex_spin_exit(lock); selclear(); continue; } /* Nothing happen, therefore - sleep. */ l->l_selflag = SEL_BLOCKING; l->l_kpriority = true; sleepq_enter(&sc->sc_sleepq, l, lock); sleepq_enqueue(&sc->sc_sleepq, sc, "select", &select_sobj); error = sleepq_block(timo, true); if (error != 0) { break; } /* Awoken: need to check the state. */ goto state_check; } selclear(); /* Add direct events if any. */ if (l->l_selflag == SEL_EVENT) { KASSERT(l->l_selret != 0); *retval += l->l_selret; } if (__predict_false(mask)) sigsuspendteardown(l); /* select and poll are not restarted after signals... */ if (error == ERESTART) return EINTR; if (error == EWOULDBLOCK) return 0; return error; } int selcommon(register_t *retval, int nd, fd_set *u_in, fd_set *u_ou, fd_set *u_ex, struct timespec *ts, sigset_t *mask) { char smallbits[howmany(FD_SETSIZE, NFDBITS) * sizeof(fd_mask) * 6]; char *bits; int error, nf; size_t ni; if (nd < 0) return (EINVAL); nf = curlwp->l_fd->fd_dt->dt_nfiles; if (nd > nf) { /* forgiving; slightly wrong */ nd = nf; } ni = howmany(nd, NFDBITS) * sizeof(fd_mask); if (ni * 6 > sizeof(smallbits)) { bits = kmem_alloc(ni * 6, KM_SLEEP); if (bits == NULL) return ENOMEM; } else bits = smallbits; #define getbits(name, x) \ if (u_ ## name) { \ error = copyin(u_ ## name, bits + ni * x, ni); \ if (error) \ goto fail; \ } else \ memset(bits + ni * x, 0, ni); getbits(in, 0); getbits(ou, 1); getbits(ex, 2); #undef getbits error = sel_do_scan(SELOP_SELECT, bits, nd, ni, ts, mask, retval); if (error == 0 && u_in != NULL) error = copyout(bits + ni * 3, u_in, ni); if (error == 0 && u_ou != NULL) error = copyout(bits + ni * 4, u_ou, ni); if (error == 0 && u_ex != NULL) error = copyout(bits + ni * 5, u_ex, ni); fail: if (bits != smallbits) kmem_free(bits, ni * 6); return (error); } static inline int selscan(char *bits, const int nfd, const size_t ni, register_t *retval) { fd_mask *ibitp, *obitp; int msk, i, j, fd, n; file_t *fp; ibitp = (fd_mask *)(bits + ni * 0); obitp = (fd_mask *)(bits + ni * 3); n = 0; memset(obitp, 0, ni * 3); for (msk = 0; msk < 3; msk++) { for (i = 0; i < nfd; i += NFDBITS) { fd_mask ibits, obits; ibits = *ibitp; obits = 0; while ((j = ffs(ibits)) && (fd = i + --j) < nfd) { ibits &= ~(1 << j); if ((fp = fd_getfile(fd)) == NULL) return (EBADF); /* * Setup an argument to selrecord(), which is * a file descriptor number. */ curlwp->l_selrec = fd; if ((*fp->f_ops->fo_poll)(fp, sel_flag[msk])) { obits |= (1 << j); n++; } fd_putfile(fd); } if (obits != 0) { if (direct_select) { kmutex_t *lock; lock = curlwp->l_selcluster->sc_lock; mutex_spin_enter(lock); *obitp |= obits; mutex_spin_exit(lock); } else { *obitp |= obits; } } ibitp++; obitp++; } } *retval = n; return (0); } /* * Poll system call. */ int sys_poll(struct lwp *l, const struct sys_poll_args *uap, register_t *retval) { /* { syscallarg(struct pollfd *) fds; syscallarg(u_int) nfds; syscallarg(int) timeout; } */ struct timespec ats, *ts = NULL; if (SCARG(uap, timeout) != INFTIM) { ats.tv_sec = SCARG(uap, timeout) / 1000; ats.tv_nsec = (SCARG(uap, timeout) % 1000) * 1000000; ts = &ats; } return pollcommon(retval, SCARG(uap, fds), SCARG(uap, nfds), ts, NULL); } /* * Poll system call. */ int sys___pollts50(struct lwp *l, const struct sys___pollts50_args *uap, register_t *retval) { /* { syscallarg(struct pollfd *) fds; syscallarg(u_int) nfds; syscallarg(const struct timespec *) ts; syscallarg(const sigset_t *) mask; } */ struct timespec ats, *ts = NULL; sigset_t amask, *mask = NULL; int error; if (SCARG(uap, ts)) { error = copyin(SCARG(uap, ts), &ats, sizeof(ats)); if (error) return error; ts = &ats; } if (SCARG(uap, mask)) { error = copyin(SCARG(uap, mask), &amask, sizeof(amask)); if (error) return error; mask = &amask; } return pollcommon(retval, SCARG(uap, fds), SCARG(uap, nfds), ts, mask); } int pollcommon(register_t *retval, struct pollfd *u_fds, u_int nfds, struct timespec *ts, sigset_t *mask) { struct pollfd smallfds[32]; struct pollfd *fds; int error; size_t ni; if (nfds > 1000 + curlwp->l_fd->fd_dt->dt_nfiles) { /* * Either the user passed in a very sparse 'fds' or junk! * The kmem_alloc() call below would be bad news. * We could process the 'fds' array in chunks, but that * is a lot of code that isn't normally useful. * (Or just move the copyin/out into pollscan().) * Historically the code silently truncated 'fds' to * dt_nfiles entries - but that does cause issues. */ return EINVAL; } ni = nfds * sizeof(struct pollfd); if (ni > sizeof(smallfds)) { fds = kmem_alloc(ni, KM_SLEEP); if (fds == NULL) return ENOMEM; } else fds = smallfds; error = copyin(u_fds, fds, ni); if (error) goto fail; error = sel_do_scan(SELOP_POLL, fds, nfds, ni, ts, mask, retval); if (error == 0) error = copyout(fds, u_fds, ni); fail: if (fds != smallfds) kmem_free(fds, ni); return (error); } static inline int pollscan(struct pollfd *fds, const int nfd, register_t *retval) { file_t *fp; int i, n = 0, revents; for (i = 0; i < nfd; i++, fds++) { fds->revents = 0; if (fds->fd < 0) { revents = 0; } else if ((fp = fd_getfile(fds->fd)) == NULL) { revents = POLLNVAL; } else { /* * Perform poll: registers select request or returns * the events which are set. Setup an argument for * selrecord(), which is a pointer to struct pollfd. */ curlwp->l_selrec = (uintptr_t)fds; revents = (*fp->f_ops->fo_poll)(fp, fds->events | POLLERR | POLLHUP); fd_putfile(fds->fd); } if (revents) { fds->revents = revents; n++; } } *retval = n; return (0); } int seltrue(dev_t dev, int events, lwp_t *l) { return (events & (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)); } /* * Record a select request. Concurrency issues: * * The caller holds the same lock across calls to selrecord() and * selnotify(), so we don't need to consider a concurrent wakeup * while in this routine. * * The only activity we need to guard against is selclear(), called by * another thread that is exiting sel_do_scan(). * `sel_lwp' can only become non-NULL while the caller's lock is held, * so it cannot become non-NULL due to a change made by another thread * while we are in this routine. It can only become _NULL_ due to a * call to selclear(). * * If it is non-NULL and != selector there is the potential for * selclear() to be called by another thread. If either of those * conditions are true, we're not interested in touching the `named * waiter' part of the selinfo record because we need to record a * collision. Hence there is no need for additional locking in this * routine. */ void selrecord(lwp_t *selector, struct selinfo *sip) { selcluster_t *sc; lwp_t *other; KASSERT(selector == curlwp); sc = selector->l_selcluster; other = sip->sel_lwp; if (other == selector) { /* 1. We (selector) already claimed to be the first LWP. */ KASSERT(sip->sel_cluster == sc); } else if (other == NULL) { /* * 2. No first LWP, therefore we (selector) are the first. * * There may be unnamed waiters (collisions). Issue a memory * barrier to ensure that we access sel_lwp (above) before * other fields - this guards against a call to selclear(). */ membar_enter(); sip->sel_lwp = selector; SLIST_INSERT_HEAD(&selector->l_selwait, sip, sel_chain); /* Copy the argument, which is for selnotify(). */ sip->sel_fdinfo = selector->l_selrec; /* Replace selinfo's lock with the chosen cluster's lock. */ sip->sel_cluster = sc; } else { /* 3. Multiple waiters: record a collision. */ sip->sel_collision |= sc->sc_mask; KASSERT(sip->sel_cluster != NULL); } } /* * sel_setevents: a helper function for selnotify(), to set the events * for LWP sleeping in selcommon() or pollcommon(). */ static inline bool sel_setevents(lwp_t *l, struct selinfo *sip, const int events) { const int oflag = l->l_selflag; int ret = 0; /* * If we require re-scan or it was required by somebody else, * then just (re)set SEL_RESET and return. */ if (__predict_false(events == 0 || oflag == SEL_RESET)) { l->l_selflag = SEL_RESET; return true; } /* * Direct set. Note: select state of LWP is locked. First, * determine whether it is selcommon() or pollcommon(). */ if (l->l_selbits != NULL) { const size_t ni = l->l_selni; fd_mask *fds = (fd_mask *)l->l_selbits; fd_mask *ofds = (fd_mask *)((char *)fds + ni * 3); const int fd = sip->sel_fdinfo, fbit = 1 << (fd & __NFDMASK); const int idx = fd >> __NFDSHIFT; int n; for (n = 0; n < 3; n++) { if ((fds[idx] & fbit) != 0 && (ofds[idx] & fbit) == 0 && (sel_flag[n] & events)) { ofds[idx] |= fbit; ret++; } fds = (fd_mask *)((char *)fds + ni); ofds = (fd_mask *)((char *)ofds + ni); } } else { struct pollfd *pfd = (void *)sip->sel_fdinfo; int revents = events & (pfd->events | POLLERR | POLLHUP); if (revents) { if (pfd->revents == 0) ret = 1; pfd->revents |= revents; } } /* Check whether there are any events to return. */ if (!ret) { return false; } /* Indicate direct set and note the event (cluster lock is held). */ l->l_selflag = SEL_EVENT; l->l_selret += ret; return true; } /* * Do a wakeup when a selectable event occurs. Concurrency issues: * * As per selrecord(), the caller's object lock is held. If there * is a named waiter, we must acquire the associated selcluster's lock * in order to synchronize with selclear() and pollers going to sleep * in sel_do_scan(). * * sip->sel_cluser cannot change at this point, as it is only changed * in selrecord(), and concurrent calls to selrecord() are locked * out by the caller. */ void selnotify(struct selinfo *sip, int events, long knhint) { selcluster_t *sc; uint32_t mask; int index, oflag; lwp_t *l; kmutex_t *lock; KNOTE(&sip->sel_klist, knhint); if (sip->sel_lwp != NULL) { /* One named LWP is waiting. */ sc = sip->sel_cluster; lock = sc->sc_lock; mutex_spin_enter(lock); /* Still there? */ if (sip->sel_lwp != NULL) { /* * Set the events for our LWP and indicate that. * Otherwise, request for a full re-scan. */ l = sip->sel_lwp; oflag = l->l_selflag; if (!direct_select) { l->l_selflag = SEL_RESET; } else if (!sel_setevents(l, sip, events)) { /* No events to return. */ mutex_spin_exit(lock); return; } /* * If thread is sleeping, wake it up. If it's not * yet asleep, it will notice the change in state * and will re-poll the descriptors. */ if (oflag == SEL_BLOCKING && l->l_mutex == lock) { KASSERT(l->l_wchan == sc); sleepq_unsleep(l, false); } } mutex_spin_exit(lock); } if ((mask = sip->sel_collision) != 0) { /* * There was a collision (multiple waiters): we must * inform all potentially interested waiters. */ sip->sel_collision = 0; do { index = ffs(mask) - 1; mask &= ~(1 << index); sc = selcluster[index]; lock = sc->sc_lock; mutex_spin_enter(lock); sc->sc_ncoll++; sleepq_wake(&sc->sc_sleepq, sc, (u_int)-1, lock); } while (__predict_false(mask != 0)); } } /* * Remove an LWP from all objects that it is waiting for. Concurrency * issues: * * The object owner's (e.g. device driver) lock is not held here. Calls * can be made to selrecord() and we do not synchronize against those * directly using locks. However, we use `sel_lwp' to lock out changes. * Before clearing it we must use memory barriers to ensure that we can * safely traverse the list of selinfo records. */ static void selclear(void) { struct selinfo *sip, *next; selcluster_t *sc; lwp_t *l; kmutex_t *lock; l = curlwp; sc = l->l_selcluster; lock = sc->sc_lock; mutex_spin_enter(lock); for (sip = SLIST_FIRST(&l->l_selwait); sip != NULL; sip = next) { KASSERT(sip->sel_lwp == l); KASSERT(sip->sel_cluster == l->l_selcluster); /* * Read link to next selinfo record, if any. * It's no longer safe to touch `sip' after clearing * `sel_lwp', so ensure that the read of `sel_chain' * completes before the clearing of sel_lwp becomes * globally visible. */ next = SLIST_NEXT(sip, sel_chain); membar_exit(); /* Release the record for another named waiter to use. */ sip->sel_lwp = NULL; } mutex_spin_exit(lock); } /* * Initialize the select/poll system calls. Called once for each * CPU in the system, as they are attached. */ void selsysinit(struct cpu_info *ci) { selcluster_t *sc; u_int index; /* If already a cluster in place for this bit, re-use. */ index = cpu_index(ci) & SELCLUSTERMASK; sc = selcluster[index]; if (sc == NULL) { sc = kmem_alloc(roundup2(sizeof(selcluster_t), coherency_unit) + coherency_unit, KM_SLEEP); sc = (void *)roundup2((uintptr_t)sc, coherency_unit); sc->sc_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_SCHED); sleepq_init(&sc->sc_sleepq); sc->sc_ncoll = 0; sc->sc_mask = (1 << index); selcluster[index] = sc; } ci->ci_data.cpu_selcluster = sc; } /* * Initialize a selinfo record. */ void selinit(struct selinfo *sip) { memset(sip, 0, sizeof(*sip)); } /* * Destroy a selinfo record. The owning object must not gain new * references while this is in progress: all activity on the record * must be stopped. * * Concurrency issues: we only need guard against a call to selclear() * by a thread exiting sel_do_scan(). The caller has prevented further * references being made to the selinfo record via selrecord(), and it * will not call selnotify() again. */ void seldestroy(struct selinfo *sip) { selcluster_t *sc; kmutex_t *lock; lwp_t *l; if (sip->sel_lwp == NULL) return; /* * Lock out selclear(). The selcluster pointer can't change while * we are here since it is only ever changed in selrecord(), * and that will not be entered again for this record because * it is dying. */ KASSERT(sip->sel_cluster != NULL); sc = sip->sel_cluster; lock = sc->sc_lock; mutex_spin_enter(lock); if ((l = sip->sel_lwp) != NULL) { /* * This should rarely happen, so although SLIST_REMOVE() * is slow, using it here is not a problem. */ KASSERT(l->l_selcluster == sc); SLIST_REMOVE(&l->l_selwait, sip, selinfo, sel_chain); sip->sel_lwp = NULL; } mutex_spin_exit(lock); } /* * System control nodes. */ SYSCTL_SETUP(sysctl_select_setup, "sysctl select setup") { sysctl_createv(clog, 0, NULL, NULL, CTLFLAG_PERMANENT | CTLFLAG_READWRITE, CTLTYPE_INT, "direct_select", SYSCTL_DESCR("Enable/disable direct select (for testing)"), NULL, 0, &direct_select, 0, CTL_KERN, CTL_CREATE, CTL_EOL); }